This invention relates in general to color television cathode ray tubes and in particular to a method of separating the glass parts of such tubes to permit salvage of tube components. Conventionally, a color television cathode ray tube has a glass bulb which is fabricated in two parts; a funnel, and a flanged faceplate which is sealed to a flared end of the funnel. The faceplate has a concave inner surface on which is deposited an electron-excitable phosphor screen and is sealed to the flared end of the funnel with a frit material which forms an airtight seal along an interface between the funnel and the flange of the faceplate. For numerous reasons, it is desirable to be able to separate the faceplate from the funnel after these glass parts have been sealed together with the frit material. For example, if a completed tube is found to have a defective internal component, separation of the funnel and faceplate permits the tube to be repaired, thereby effecting substantial cost savings.
A well established method of salvaging glass parts from a conventional cathode ray tube involves a process of thermally shocking ("thermoshocking") either the faceplate flange or the funnel alternately with cold and hot water in order to separate the faceplate and funnel.
Thermal shocking of the glass bulb typically is achieved by down-shocking (application of water with a temperature lower than an initial bulb temperature to cause a sudden cooling of the surface of the bulb) or up-shocking (application of water with a temperature which is higher than an initial bulb temperature to cause a sudden heating of the surface of the bulb). This causes the part which has been shocked to flex, thereby causing tension at the sealing interface and a subsequent cleavage through and parallel to the sealing interface. Generally, before thermoshocking the tube, any excess frit material on the outside of the bulb around the sealing interface is etched away by submerging the tube in a nitric acid bath or by spraying nitric acid onto the frit material. Such a method as described above is disclosed in U.S. Pat. No. 2,884,312 to Kuryla. Another related method of separating glass bulbs is disclosed in U.S. Pat. No. 3,390,033 to Brown.
A unique bulb for a color television cathode ray tube is disclosed in U.S. Pat. No. 3,894,260, issued to the assignee of this application. The bulb has a flangeless, curved, glass faceplate with a concave inner surface. The funnel portion of this unique bulb has a convex, curved seal land; that is, a seal land which defines a convex, curved plane which matches and mates with the curvature of the concave inner surface of the faceplate. Since the faceplate is flangeless, the sealing interface between the funnel and the faceplate is curved rather than planer as in conventional tubes.
Attempts to salvage glass parts from this bulb by prior art methods such as described above have resulted in excessive glass breakage. If the faceplate only is shocked, glass is broken out of the funnel at the sealing interface. If the funnel is shocked, separation is usually not achieved because the funnel shape is too rigid for sufficient flexure at the sealing interface. If an attempt is made to shock both the flangeless faceplate and the funnel simultaneously to gain sufficient flexure from both parts, glass is frequently broken out of the funnel seal land from the long side and toward a corner, especially if there is heavy frit material in these areas along the sealing interface on the inside of the bulb.
A crack in glass will usually propagate along a path of maximum tension. With the unique bulb described, if the faceplate and the entire perimeter of the funnel wall adjacent to the sealing interface are shocked, initial separation will usually occur on a short side of the funnel and propagate around a corner to an adjacent long side. As the crack rounds the corner and approaches the long side, the crack departs from the curved plane of the sealing interface since it recognizes a higher tension zone in the funnel glass, which zone may be created by the existence of a heavy deposit of frit material at the sealing interface in that region. If the initial separation is caused to originate on the long side of the funnel, a similar problem of glass breakage on a short side and toward a corner is encountered. Therefore, in general, known prior art methods of salvaging parts from color television cathode ray tube bulbs of the conventional type having a flanged faceplate are not suitable for salvaging bulbs of the type disclosed in U.S. Pat. No. 3,894,260.